1. Field of the Invention
The present invention generally relates to a microcomputer. More specifically, the present invention is directed to a microcomputer chip into which a function capable of supporting emulation has been assembled, a semiconductor device on which the above-explained microcomputer chip has been mounted, and an emulator for performing emulation of this microcomputer chip.
2. Description of the Related Art
In a microcomputer (to be referred to as “single chip microcomputer” hereinafter) which mounts thereon a program storing-purpose memory as a ROM, a software program to be installed in the single chip microcomputer needs to be developed. In order to develop and debug the above-described software program, an “emulator” has been conventionally used. The emulator emulates a function of the microprocessors, and provides an environment for debugging the operation of the software program and confirmations of the operation of a hardware circuit. For this purpose, the emulator is provided with a chip for emulating the function of a product, and an “evaluation chip” for controlling the chip. As the emulator, for example, “ICE (In-Circuit Emulator: registered trademark)” is known. Also, an operation for developing and debugging a software program by use of an emulator is referred to as “emulation.”
When an emulator is constructed, a chip for emulating the functions of a product chip is necessary. However, it is not desired to develop this emulation chip separately from the product chip, in view of a cost-to-effect aspect. For this reason, it is proposed to incorporate the function for supporting the emulation in the product chip. In this case, since this supporting function is no longer required at a time of shipping the product chip, it is desired to suppress increase of a chip area through adding this supporting function.
As general-purpose techniques capable of suppressing the increase of the chip area, the following techniques are known.
That is, Japanese Patent Laid Open Patent Application (JP-A-Heisei 3-173433: a first conventional example) discloses a semiconductor integrated circuit device in which pads are arranged at a peripheral portion of a chip, and are electrically connected to external terminals. In this semiconductor integrated circuit device, these pads are arranged in two or more lines along the edges of this chip. Further, at least two layers are formed in a thickness direction of the chip to constitute internal wiring lines for electrically connecting the pads to an internal circuit. Also, in this conventional example, the pads other than the pads in the outermost line are used as test terminals, which are used to test LSI functions in a wafer stage. For this reason, the bonding wire is not connected to the test terminal. Only the pads in the outermost line are electrically connected to the external terminals.
Also, Japanese Laid Open Patent Application (JP-P2002-299567A: second conventional example) discloses a semiconductor device in which electrode pads are arranged and formed on a partial structural element of an integrated circuit formed on a semiconductor wafer. This structure is referred to as a “CUP (Circuit Under Pad).”
A microcomputer into which a function for supporting emulation is incorporated is packaged and then is connected to an emulator. In other words, the microcomputer contains a circuit interfacing with the emulator at least. Electrode pads used to connect this circuit with the external emulator are referred to as “emulation pads.” On the other hand, electrode pads for normal use are referred to as “product pads.”
In order to suppress increase of a chip area, it could be considered that that product pads are commonly used as emulation pads. The common pads are connected to switch circuits, which control the common pads to be connected to the normal circuit and the emulation circuit in response to control signals. For instance, it is assumed that a microcomputer chip has a first pad connected to the switch circuit. In this case, the first pad is connected to the emulation circuit when a software program is developed. For this reason, a function of a port connected to the first pad in the normal operation cannot be confirmed. Therefore, in order to confirm this function, another microcomputer chip having a second pad different from the first pad and connected to a switch circuit must be prepared separately from the microcomputer chip. In this way, although increase of the chip area can be avoided if the electrode pads are commonly used to the emulation pads, sorts of chips to be prepared are increased.